Inhibiting popcorn polymer formation



3,265 752 INHIBITING POPCORN POLYMER FORMATION Alfred Case Whiton, Blue Bell, and Harry Elmer Albert, Lafayette Hill, 'Pa., assignors to Pennsalt Chemicals Corporation, Philadelphia, Pa., a corporation of Pennsylv'ania No Drawing. Filed Dec. 17, 1964, Ser. No. 419,224

3 Claims. (C|. 260-666.5)

This invention relates to the inhibition of the undesirable polymerization of olefinic monomers which give rise to popcorn polymers. The invention is particularly concerned with the use of a mixture of N-hydroxymorpholine with an N,N-dialkylhydroxylamine as a popcorn polymer inhibitor in processes relating-to the preparation of synthetic rubber.

US. 3,148,225 which issued September 8, 1964, discloses the use of N,N-dialkylhydr oxylamines as popcorn polymer inhibitors. It has now been found, however, that N-hydroxymorpholine may be used in conjunction with N,N-dialkylhydroxylaminesto inhibit popcorn polytained. We have found thatthe combination of'N-hydroxymorpholine with the N,N-dialkylhydroxylamines is ,alkylf is meant-to include cycloalkyl as well as acyclic alkyl and thus R and R, will include methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tertbutyl, amyl, hexyl, cyclohexyl and the like. It will also be understood that R, and R may be the same or different in the same molecule of N,N-di-alkylhydroxylamine.

The general conditions under which the olefin monomers are contacted with the inhibitors in accord with this invention will be those procedures setforth in US. 3,148,225 referred to above. Likewise, the olefin monomer recovery systems which are subject to the treatment in accordance with this invention will be those systems where polymers and copolymers are obtained from eth: ylenically unsaturated monomers, and will include those systems described in US. 3,148,225.

mer formation with an effectiveness not heretofore ob- Preferably, the invention will be used to prevent popsynthetic rubber and the invention will be illustrated by examples referring to this system. The concentration at which the inhibitor mixture will be used will usually range from 0.001 to about 5.0% of total inhibitors by weight of the total monomers; i.e. from about 10 to 50,000 parts per million parts of monomer. At concentrations below this value the inhibitingetfects are too small to be of significant value. 0n the other hand, greater amounts maybe used say up to 20% but such large amounts are not required and are simply wasteful.

The N-hydroxymorpholine will be used. in conjunction with the N,N-dialkylhydroxylamine as described above at a weight ratio of N-hydroxymorpholine to N,N-dialkylhydroxylamine of from about 10:90 to about 90:10. Preferably, however the weight ratios at which the agents will be used will vary between 25:75 and 75:25.

3,265,752 Patented August 9, 1966 As will be seen from the examples which follow, the I EXAMPLE 1 i The procedure for evaluating the effectiveness of the popcorn polymer inhibitors of this invention is similar to that disclosed in US. 3,148,225 except that the popcorn polymer seed is activated prior to introduction into the atmosphere where popcorn polymer formation can occur.

This activation is carried out by exposing the popcorn polymer seed to a watt incandescent lamp for about 12 hours prior to its introduction into the polymerization atmosphere.

The technique in detail is as follows:

Bottles are flushed with nitrogen and then changed with 30 milliliters of inhibitor free styrene, 0.5 g. of popcorn polymer seed and the material to be tested as the popcorn inhibitor. The seed is that taken from a styrenebutadiene rubber flash tank and it is activated just before use by exposing it overnight to a 100 watt incandescent lamp. The 'bottles are then capped and l milliliter of butadiene is injected into each bottle with a hypodermic syringe through a self sealing synthetic rubber cap liner. The bottles are then placed in a constant temperature oven at F. and are inspected periodically for the appearance of popcorn polymer. After popcorn growth starts in each bottle it usually proceeds rapidly, filling the free space in the bottle nearly full within hours with a white insoluble polymer having the appearance of popcorn.

The following table indicates the test conditions and the results obtained:

Table 1 EFFECT OF POPCORN POLYMER INHIBITORS EVALUATED AT 140 F.

Inhibitor (percent by weight Time required to of total monomers):

observe popping None, hours 12 0.05% diethylhydroxylamine, days 1.5 0.10% diethylhydroxylamine, days 2.5 0.05% N-hydroxymorpholine, days 11 0.05% N-hydroxymorpholine plus 0.05% dieth ylhydroxylamine, days 16 It will be observed from a study of the above table that the combinatio'n of diethylhydroxyla-mine and N-hydroxymorpholine inhibits popcorn polymer formation for 16 days while the data would indicate that such a combination should give an additive effect of 12.5 days. Thus, the synergistic combination is obvious.

Instead of using N,N-diethylhydroxylamine in the above examples, N,N-dimethylhydroxylarnine, N,N-didialkylhydroxylamine containing from one to six carbon atoms in each alkyl group.

' 2. The process of inhibiting popcorn polymer formation from monomers used in the preparation of a butadiene based elastomer which comprises contacting said monomers with about 0.001% to about 5% by weight -elf-said monomers with a mixture comprising N-hydroxymorpholine and an N,N-dialkylhydroxylamine containing from one to six carbon atoms in each alkyl group, said N-hydroxymorpholine and said N,N-dialkyihydroxy1- amine being at a weight ratio from 10:90 to 90: 10.

3. The process of inhibiting popcorn polymer formation from monomers used in the preparation of a styrenebutadiene elastomer which comprisescontacting said monomers with an inhibiting amount of a mixture comprising N-hydroxymorpholine and N,N-diethylhydroxylamine, said N-hydroxymorphoiine and N,N-diethylhydroxylamine being at a weight ratio of from 25:75 to 75:25.

References Cited by the Examiner UNITED STATES PATENTS 3,148,225 9/ 1964 Albert 260-6665 X DELBERT E. GANTZ, Primary Examiner. G. E. SCHMITKONS, Assistant Examiner. 

1. THE PROCESS OF INHIBITING POPCORN POLYMER FORMATION IN OLEFIN MONOMER RECOVERY SYSTEMS WHICH COMPRISES CONTACTING SAID MONOMER WITH AN INHIBITING AMOUNT A MIXTURE COMPRISING N-HYDROXYMORPHOLINE AND AN N,NDIALKYLDROXYLAMINE CONTAINING FROM ONE TO SIX CARBON ATOMS IN EACH ALKYL GROUP. 